Long-term nutrient cycling patterns in Douglas-fir and red alder stands: a simulation study |
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| Institution: | 1. Departamento de Agronomia, Universidade Federal Rural de Pernambuco (UFRPE), Recife, Pernambuco, Brazil, 52171–900;2. Dipartimento di Biologia, Ecologia e Scienze della Terra, Università della Calabria, Cosenza, Italy, 87036;3. Department of Environmental Research and Innovation, Luxembourg Institute of Science and Technology, Esch–sur–Alzette, Luxembourg, 4422;4. Departamento de Ciência do Solo, Universidade Federal Rural de Pernambuco (UFRPE) – Unidade Acadêmica de Garanhuns, Garanhuns, Pernambuco, Brazil, 55292–270;5. Departamento de Ciência do Solo, ESALQ– Universidade de São Paulo, Piracicaba, São Paulo, Brazil, 13418, –900;1. RISKNAT group, Geomodels Institute, Departament de Dinàmica de la Terra i de l''Oceà, Facultat de Ciències de la Terra, Universitat de Barcelona (UB), Martí i Franquès s/n, 08028 Barcelona, Spain;2. ICGC, Institut Cartogràfic i Geològic de Catalunya, Parc de Montjuïc, 08038 Barcelona, Spain;3. Centre Mediterrani d''Investigacions Marines i Ambientals-CSIC, Psg. Marítim de la Barceloneta, 37-49, 08003 Barcelona, Spain |
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| Abstract: | Long-term patterns in nutrient cycling in regrowing Douglas-fir (Pseudosuga menziesii Mirb. Franco) and red alder (Alnus rubra Bong.) on native soils plus soils previously occupied by other species were simulated using the nutrient cycling model. Simulations of regrowing stands were also compared with observations of nutrient cycling in mature Douglas-fir and red alder. We hypothesized that (1) prolonged presence of red alder will cause a depletion in soil base cations due to increased nitrification and NO3? leaching; (2) lower base cation availability under red alder will ultimately cause biomass production to decline; (3) high N availability in red alder soils will favor regrowth of Douglas-fir; (4) higher base cation and P status of the Douglas-fir soils will favor growth of red alder both in the short- and long-term, since N is not limiting to red alder; and (5) in regrowing red alder, NO3? leaching will increase with time as a result of increased N fixation. All hypotheses were confirmed, but the effect of soil type on biomass production was minimal both for red alder and Douglas-fir. The higher soil organic matter content in the mature red alder stand most likely reflected previous occupation by old-growth Douglas-fir and also a large litter input from the understory vegetation. In general, the nutrient cycling model simulated differences in nutrient cycling patterns at least qualitatively between Douglas-fir and red alder and was helpful in identifying potential gaps in the understanding of biogeochemical cycling as well as uncertainties in the data. The nutrient cycling model did not fully elucidate differences in P cycling between Douglas-fir and red alder and overestimated weathering rates under Douglas-fir. Uncertainties in the data included: (1) temporal patterns in N fixation in the regrowing stands; (2) understory litterfall; and (3) site history and, consequently, presence of pre-existing differences in site conditions. |
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